268 Mr. Herapath on True Temperature, and the [Oct. 



ber, but more massy particles. The particles of this new air 

 being greater would, at the same temperature, have a less velo- 

 city, which would alone, if the figures of the particles disposed 

 them to it, tend very much to promote a further aggregation. 

 Independent of this, the superior action of the particles resulting 

 from their increased masses, if aided by a sufficient mutual 

 adaptation of figure, would produce other unions, though it 

 should be at a considerable elevation of temperature ; and if the 

 resulting particles have yet adaptation enough, the unions 

 may be carried to a still greater length. However, it may hap- 

 pen that after one or two unions only the masses of the particles 

 may become too great to enable them to be reflected with a 

 «ufficient velocity to preserve their aeriform property, and then 

 of course a condensation will immediately follow. Under any 

 circumstances, if the temperature and successive figures favour 

 it, a condensation will be the consequence. This is the most 

 general view that can well be given of the cause of condensation] 

 There are, however, other circumstances which might contribute 

 towards, or effect it, that I may hereafter explain. 



If this theory of vapours be granted, it follows that the whole 

 difference between gases and vapours consists in the figures of 

 their component particles, and that, therefore, vapours uncon- 

 nected with their fluids at all higher temperatures than those at 

 which they would condense, have the same laws of expansion 

 and contraction as gases, which agrees with the experiments 

 of Mr. Dalton ; for he has found that their elasticity uncon- 

 nected with the fluids from which they are formed, increases 

 or diminishes with their temperature ; and that their bulk 

 undergoes precisely the same increase which air does under 

 the same circumstances and change of temperature. These 

 two laws, especially the last, are a decided demonstration 

 of the views I have developed, and authorise, therefore, the 

 admission to vapours of all the laws of gases I have demonstrated 

 in my last paper. 



When any number of equal volumes of different gases having 

 no chemical action are mixed at the same temperature, the elas- 

 ticity of the compound mass reduced to the same volume is equal 

 to the sum of the elasticities of all the component gases. This 

 theorem, which experiment has confirmed, is not demonstrated 

 in my last paper ; but it is a very easy consequence of what I 

 have there delivered. Hence vapours above certain temperatures 

 being of the same nature, and following the same laws of dilata- 

 tion as gases, the same law of elasticity will likewise hold good in 

 a similar mixture of any number of vapours, or of any number of 

 vapours and gases, provided no chemical action takes place. 

 This conclusion has been experimentally proved both, I believe, 

 by Mr. Dalton and M. Gay-Lussac. 



From the experiments of Mr. Sharpe and of Mr. Southern, it 



